1. Field of the Invention
The present invention relates to a surface processing method, and in particular to a surface processing method for a high hardness and abrasion resistant zinc alloy surface of imitation plating hexavalent chromium.
2. The Prior Arts
Presently on the market, the zinc alloy chromium plated products are plated with hexavalent chromium, and that are produced through the conventional electroplating. However, the conventional electroplating of zinc alloy has the following drawbacks and shortcomings: 1. It consumes large amount of water and energy, to produce large amount of waste water and waste scum, such that its waste treatment expense is high. 2. It utilizes detrimental chemical plating solutions and additives. 3. It could produce toxic gases in the production process. 4. It consumes large amount of metal. 5. It utilizes hexavalent chromium, and that is harmful to the human body.
In this respect, bubbles often occur in the plated layer of hexavalent chromium for the zinc alloy, such that the plated layer tends to detach from and fall off the substrate. Moreover, the casting and pressing of the zinc alloy can greatly affect the quality of the electroplating, such that the plated surface is not allowed to have the defects of loose texture, crack wrinkles, air holes, air bubbles, shrunken holes, cold wrinkles, and needle holes, etc., otherwise, it could lead to defective outer appearance of the electroplated layer, and the problem of unsatisfying performance.
In this respect, the various shortcomings and drawbacks of the prior art are described as follows:
In a China Patent Case No. CN 102758237A is disclosed “surface processing method for a high etch resistance zinc alloy of imitation hexavalent chromium color”, including the following steps:
1. Perform ultrasonic de-wax and de-grease treatments for a zinc alloy blank.
2. Perform anode oxidation processing, for the zinc alloy blank processed by step 1.
3. Perform electrophoresis application, water washing, and baking and drying processing for the zinc alloy blank processed by step 2.
4. Transfer the zinc alloy blank processed in step 3 to a paint spraying and ultraviolet light (UV) curing line, to perform UV primer (bottom paint) spraying, leveling, and UV curing.
5. Hang the zinc alloy blank processed by step 4 into a physical vapor deposition (PVD) furnace to perform plasma processing, and then perform film plating processing through PVD.
6. Perform intermediate layer paint spraying, for the zinc alloy blank transferred into the paint spraying and UV curing line, and then perform leveling and UV curing. Subsequently, perform spraying of transparent UV surface paint, leveling, and UV curing. In the process of curing the intermediate layer paint using UV light, the color of the plated hexavalent chromium can be obtained, to complete surface processing of high etch resistance zinc alloy having imitated color of hexavalent chromium.
The surface processing method of the imitation hexavalent chromium color adopts a thermal curing electrophoresis primer, with its curing temperature at 140-170° C. However, in the casted and pressed zinc alloy piece, blister nests are liable to exist. In a baking temperature of 140-170° C., the electrophoresis application layer tends to produce craters and pits, such that its outer appearance is defective, its yield is low, the hardness of the plated layer and its abrasion resistance are insufficient. In addition, that patent case utilizes large quantity of chemicals to remove wax and grease on the surface of the zinc alloy, thus producing large amount of waste water.
In another China Patent Case No. CN 102758176A is disclosed “An all dry composite film plating method for a metal surface”. In that patent, surface processing is performed for the imitation plating hexavalent chromium, directly on a polished surface of a metal substrate. The demand for polishing the metal substrate is rather high, since the polished surface has to be as glaring as a mirror. In this respect, that patent is not capable of eliminating the blister nests on the surface of the casted and pressed zinc alloy piece.
Therefore, presently, the design and performance of a surface processing method for a zinc alloy surface of imitation plating hexavalent chromium is not quite satisfactory, and it has much room for improvement.